Gasification of carbonaceous solid fuels



June 29, 1954 E. GORIN 2,682,455

GASIFICATION OF CARBONACEOUS SOLID FUELS Filed June 16, 1949 5 Sheets-Sheet 1 FIG.

TEMPERATURE PRESSURE (ATM) INVENTOR EVERETT GORIN g 'ZMja.

TTORNEY June 29, 1954 E. GORlN GASIFICATION OF CARBONACEOUS SOLID FUELS Filed June 16, 1949 5 Sheets-Sheet 2 IPRODUCT GAS FIG. 2

STEAM L STEAM J A DRAWOFF INVENTOR EVERETT GORIN A ORNEY June 29, 1954 E. GORIN GASIFICATION OF CARBONACEOUS SOLID FUELS 5 Sheets-Sheet 4 Filed June 16, 1949 w o hoacomm OON INVENTOR EVERETT GORIN BY .1? [M1 ATTORNEY June 29, 1954 E. GORIN 5 GASIFICATION OF CARBONACEOUS SOLID FUELS Filed June 16, 1949 5 Sheets-Sheet 5 PRODUCT GAS CHAR

T0 REGENERATOR 5 TORNEY Patented June 29, 1954 GASIFICATION OF CARBONACEOUS SOLID FUELS Everett Gorin, Castle Shannon, Pa.., assignor to Pittsburgh Consolidation Coal Company, Pittsburgh, Pa., a corporation of Pennsylvania Application June 16, 1949, Serial No. 99,561

4 Claims. (Cl. 48-19'7) This invention relates to the gasification of carbonaceous solid fuels and, more particularly, to methods of and apparatus for reacting carbonaceous solid fuels with steam.

The present application is a continuation-inpart of my copending application Serial Number 58,132, filed November 3, 1948, and now abandoned. v

The primary object of this invention is to provide an improved process for converting carbonaceous solid fuels into a gaseous product by reaction with steam.

Another object of this invention is to provide a process in which steam reacts with solid carbonaceous fuels to yield a gaseous product under such conditions that no heat need be added to the system, i. e., under thermoneutral conditions.

A further object of this invention is to provide an improved process for making a high B. t. u. fuel gas which is rich in methane.

Still another object of the present invention is to provide an improved method for converting carbonaceous solid fuels into a gas which is rich in hydrogen and which is substantially free of carbon dioxide.

For an understanding of my invention, reference should be had to the following description and to the accompanying drawings, in which:

Figure 1 is a graphical illustration of the critical relationship between pressure and temperature which governs the operation of my invention;

Figure 2 is a diagrammatic illustration of an apparatus comprising a one-vessel system adapted to carry out the preferred embodiment of my invention;

Figure 3 is a diagrammatic illustration of an apparatus comprising a multiple-vessel system adapted to carry out a modification of the preferred embodiment of my invention;

Figure 4 is a diagrammatic illustration of an apparatus adapted to carry out another modification of the preferred embodiment of my new process; and

Figure 5 is a diagrammatic illustration of an apparatus adapted to carry out a still further modification of my new process.

In accordance with my invention, I utilize the reaction between steam and carbon to convert solid carbonaceous fuels into a gaseous product in the presence of calcium oxide. Calcium oxide previously has been used in the water gas reaction in relatively small amounts as a catalyst or carbon dioxide acceptor. However, I have discovered that when calcium oxide is mixed with carbonaceous solid fuels in the proper proportions and under certain critical conditions of temperature and pressure, the steam-carbon reaction is thermoneutral; i. e., no heat need be added to the system to maintain the reaction. In fact, the reaction may even be exothermic and capable of generating the steam necessary for the process. Moreover, it was found that under these thermoneutral conditions, gases which contain unexpectedly high percentages of either methane or hydrogen can be selectively produced by operating under conditions lying within the critical range required to produce a thermoneutral reaction.

More specifically, my new process comprises the use of calcium oxide and finely divided carbonaceous solid fuels in the proportions of at least 120 parts by weight of calcium oxide to parts by weight of carbon contained in the fuels. This mixture is reacted with steam at a temperature between 1430 and 1800 F. I have discovered, however, that there is a minimum pressure which must be attained in order that the overall reaction be thermally self-sufficient; i. e., at least thermoneutral and preferably exothermic. This minimum pressure is a function of the reaction temperature and, in the temperature range from 1430 to 1800 F., is expressed by the empirical relation (1) p=3.40-1.89 10 (t1430)+ 448x10-*(t1430) where p is the pressure in atmospheres and t is the reaction temperature in F.

The gas producing process of my invention may be operated thermoneutrally provided the minimum pressure is that defined by Equation 1. However, I have found that when the operating pressure is increased above the minimum value at a constant temperature, the proportion of methane in the gas produced increases while the proportion of hydrogen correspondingly decreases. Thus, at constant temperature, the composition of the product gas varies with the operating pressure.

If then a methane rich, high B. t. u. gas product is desired, there is a second minimum operating pressure, arbitrarily chosen which must be exceeded in order that the heating value of the product gas (a measure of the methane content) will exceed 400 B. t. u. per cubic foot. This minimum pressure also can be expressed as an empirical function of the reaction temperature by (2) p=5.0+4.2 10 (t-1430)+ 3 where p is the pressure in atmospheres and t is the temperature of the reaction zone in F.

Equations 1 and 2 are shown graphically in Figure 1. The improved process of my invention will produce a hydrogen rich gas when the operating pressure lies between the curves representing Equation 1 and 2 as determined by the reaction temperature.

A methane rich, high B. t. u. gas can be produced when the operating pressure lies above the curve representing Equation 2 as determined by the reaction temperature. The process of my new invention will produce a methane rich gas within the temperature range from 1430 to 1800 F., but I prefer to produce methane rich gas within the temperature range from 1520 to 1650 F., and at a corresponding pressure ranging from 10 to 40 atmospheres, the pressure being at least that determined by Equation 2 depending upon the operating temperature.

A hydrogen rich gas can be produced in a thermoneutral reaction by my new invention within the temperature range from 1430 to 1800 F., but I prefer to produce hydrogen rich gas within the temperature range from 1520 to 1650 F., at a pressure corresponding to the temperature of the reaction, within the range from 5 to about 30 atmospheres provided, however, the pressure is at least that given by Equation 1 and is less than that given by Equation 2 according to the temperature employed.

It should be stressed at this point that the process of my new invention will operate to produce a gas by a thermoneutral steam-carbon reaction so long as the pressure is at least that given by Equation 1.

In the preferred embodiment of my invention, the reaction between steam and carbonaceous solids is carried out in a single vessel system utilizing an on-and-off cycle. Steam is passed through a bed of calcium oxide and the carbonaceous solids to yield a gas containing hydrogen, methane, carbon monoxide and carbon dioxide. Simultaneously calcium carbonate is formed in the vessel from the reaction between calcium oxide and the carbon dioxide in the gas produced. During the off cycle, air or any gas containing oxygen gas is circulated through the vessel to regenerate the calcium oxide from the calcium carbonate. Sufficient carbonaceous solids are oxidized during the regeneration cycle to raise the temperature of the carbonate above its dissociation temperature so that the carbonate decomposes into calcium oxide and carbon dioxide.

While I prefer to use a non-fluidized system, nevertheless a fluidized system may be employed which comprises either a single vessel or a plurality of vessels as will be described in detail later. Whether the system is fluidized or nonfluidized, the yield of methane can be increased in my new process by deliberately establishin a temperature gradient through the steam-carbon reaction vessel in a manner which will be described in detail later. In this modification of my invention, the steam-carbon reaction is first carried out at a temperature preferably between 1670 and 1770 F. and the products therefrom are then passed in contact with carbonaceous solids at a lower temperature, preferably between l430 and 1600 F. A large increase in methane production thereby results.

The yield of hydrogen, on the other hand, when the process is operated under the condition set forth to produce hydrogen rich gas, can be further increased according to the conventional water gas shift reaction in which carbon monoxide and steam react to produce carbon dioxide and hydrogen. When the water gas shift reaction is conducted at temperatures in the range of 1200 to 1500 F. in the presence of lime, the carbon dioxide resulting from the shift is removed by the lime forming calcium carbonate. Since the main constituent (other than hydrogen) of the water gas produced by the process of my invention is carbon monoxide, the second reaction, in which substantially all the carbon monoxide is converted to hydrogen serves to produce a gas far richer in hydrogen than any previously made in a steam-carbon reaction.

In certain instances it may be desirab1e to accelerate the steam-carbon-calcium oxide reaction by the addition of catalytic materials. For example, the oxide is impregnated with amounts of the order of one to ten parts byweight of an oxide of the transition group metals, such as iron, nickel, cobalt, manganese, etc.; or on the other hand, small amounts of an alkali or heavy alkaline earth carbonate, such as sodium carbonate, barium carbonate, etc. may be employed. Also certain other alkaline earth oxides may be incorporated with the lime to increase its physical strength, e. g., MgO as in dolomite.

In the following description of a specific embodiment of my invention, by way of example only, my new process is applied to the carbonaceous solid residue obtained by the low temperature distillation or carbonization of hydrocarbonaceous solid fuels such as the high volatile bituminous coal found in the Pittsburgh Seam. This residue, for the purpose of convenience, I shall hereafter refer to as char. It is to be understood, however, that the process is generally applicable to any carbonaceous solid fuels which react with steam to produce water gas. Among such carbonaceous solids are included all ranks of coal, lignite, oil shale, tar sands, coke from coal or petroleum pitch, solid tar, etc. Highly reactive solid fuels such as char and lignite are preferred because of the relatively moderate temperature at which the process is operated.

The apparatus shown in Figure 2 and its operation will now be described. A mixture of char and lime is introduced into a reaction vessel ID of any suitable type adapted to retain a bed of solids at elevated temperatures and high pressures. The mixture of lime and char is obtained by charging lime and char in the proper proportions from their respective supply hoppers I2 and [4 to a mixing chamber IS in which the two batches of solids are thoroughly mixed. From the mixer 16 the solids are transferred to the vessel H] through a conduit l8 by a motor driven screw feeder 20. The relative amounts of char and lime in the mixture are. regulated so that the resulting bed 22 in reaction vessel I0 contains at least 120 and preferably between 120 and 300 arts by weight of lime for every parts by weight of carbon contained in the char. In order to raise the temperature of the bed to a point between 1430 and 1800 F., air is introduced through suitably valved conduits 24. A small amount of carbonaceous solids is burned by the air to supply the heat required to attain the temperature of the bed previously specified.

When the temperature of the bed 22 has reached the desired temperature in the range from 1430 to 1800 F., the flow of air through conduits 24 is discontinued andv steam is introduced into vessel H) through suitably valved conduits 26.

At the same time a valve 28 in the gaseous product line 30 is regulated so that the pressure within vessel ID will be at least as high as the minimum pressure calculated from the followin relation where p is the pressure in atmospheres and t is the temperature in F.

The pressure in vessel II) should be at least as high as the minimum thermoneutral pressure calculated from Equation 1 when a product is desired with maximum hydrogen content and should lie within the area bounded by curves (1) and (2) of Figure 1. The pressure is preferably within the range from 5 to 30 atmospheres from the production of a hydrogen rich gas. On the other hand, if a methane rich gas is desired, the pressure in vessel Ill should exceed that given by Equation 2 and preferably should lie within the range from to 40 atmospheres selected so that the pressure lies within the area above curve (2) as shown in Figure 1.

Steam passing up through bed 22 reacts with char to produce carbon monoxide, hydrogen, methane and carbon dioxide. The carbon dioxide contained in the product gas reacts with the lime in the bed 22 to produce calcium carbonate and to liberate heat. Under the conditions of temperature and pressure determined by the relation above, the heat developed by the reaction of the carbon dioxide with the lime is suflicient to maintain the temperature of the tion, is returned to hopper l2 for recirculation through the reaction zone. If desired, instead of an intermittent operation as described, the screws 20 and 34 may be operated continuously. In this case, the withdrawn carbonate is converted to lime in a separate vessel by blowing air through a bed of withdrawn ash and carbonate; the regenerated lime then is separated from the ash as before and returned to the lime 10 supply hopper I2.

The gas produced, substantially free of carbon dioxide, is conveyed through conduit 30 to any suitable point for further treatment or for immediate use or storage. It should also be pointed out that this product gas is relatively free from sulfur contamination because of the reaction of lime with sulfur containing components of the gas producing solid sulfides which remain in vessel Ill. The resulting sulfides are removed along with the ash through drawoff conduit 32.

The following table lists the percentages of each of the components of the dry gas product as produced under different sets of temperature and pressure. Under heading (A) is shown the composition of the gas produced in the presence of lime under conditions of temperature and pressure favoring the production of hydrogen rich gas. It should be noted that when lime is used in accordance with my invention, the hydrogen content is greatly increased. Heading (B) shows the composition of the gas produced in the presence of lime under the critical conditions of the present invention. The increase in methane content achieved by the method of my invention will be observed.

Table I WITHOUT LIME Percent Gas Compositions Gross Heat- Tem atirature, fig OSteam Bilig Value,ft

. onveru. cu. Abmlute sion H2 CH4 00 002 at 60 F.

WITH LIME (A) [At pressures selected to produce hydrogen rich gas] WITH LIME (B) [At higher pressures selected to produce methane rich, high B. t. u. gas] bed within the desired operating range and. to provide the heat necessary for the endothermic reaction of the steam with the char. When steam has reacted with substantially all the carbonaceous fuel in the bed 22, the flow of steam into vessel l0 through conduit 26 is discontinued; the pressure in the vessel is reduced to atmospheric; and air is introduced through conduits 24. The combustion of the remaining fuel with oxygen from the air provides the heat required to regenerate the lime by liberating carbon dioxide from the carbonate. The regenerated lime and ash are then withdrawn from vessel I0 through conduit 32 by means of a motor driven screw feeder 34. The lime, after its separation from the ash by any suitable manner, such as elutria- It will be noted that when water gas is produced using lime in accordance with my invention, there is a considerable improvement in the hydrogen content of the gas as compared with the production of water gas without lime when the operating pressure is only slightly higher than the minimum pressure as determined from the empirical relation above. It should be further noted that where the operating pressure is substantially greater than the minimum in the presence of lime, the methane content of the product gas is greatly increased over that of the gas produced without lime.

The per cent steam conversion is given in each of the above examples in Table I in order to permit a valid comparison to be made. The

amount of this conversion is determined by the residence time as is well known. However, in the casewhere no lime is used the maximum obtainable conversion is increased to 91 per cent. This is '77 per cent while under the same conditions, where lime is employed, the maximum. obtainable conversion is increased to 9| per cent. This marked increase in per cent steam conversion is also observed at other conditions of temperature and pressure within the critical range of the present invention.

It will thus be apparent that by proper selection of operating conditions within the above defined limits, it is possible to produce by a thermoneutral process a gas containing hydrogen, methane and carbon monoxide in a wide range of different relative proportions. Under certain selected conditions, a gaseous mixture may be produced in which the Hz/CO ratio is approximately 2/1. synthesis gas for a Fischer-Tropsch conversion to liquid hydrocarbons.

In the operation of the apparatus shown in Figure 2 the regeneration of the lime was indicated as being carried out in a non-fluidized system. However, it is desirable wherever possible to regenerate the lime in a fluidized operation in order to obtain good heat control. While it is possible to effect the steam-carbon reaction in a fluidized bed at relatively low pressures, it is not always possible to do so when operating at the high pressures preferred in my new process. The difficulty arises from the fact that, at the linear velocities required to maintain fiuidization, deep beds are needed to obtain the necessary contact time at elevated pressures.

A system may accordingly be employed in which the steam-carbon reaction is carried out in a non-fluidized bed while the regeneration of the lime is effected in a fluidized bed. The non-fluidized bed should rest upon a distribution plate to disperse the incoming steam uniformly over the base of the bed. The particle size range of the solids must be such as to permit fluidized operation in the regeneration cycle and non-fluidized operation in the steam-carbon reaction cycle; i. e., to +200 mesh. For example, when one operates at about 20 to atmospheres, linear velocities of the order of 0.01 to 0.05 foot per second may be employed in the steam cycle.

The fluidized lime regeneration process on the other hand, is carried out at substantially atmospheric pressure with linear velocities of air of the order of 1.0 foot per second. The regeneration vessel has a much higher capacity than the steam-carbon reaction vessel and therefore one regeneration vessel may be employed in conjunction with anywhere from four to ten steamcarbon reaction vessels.

Such a system is shown in Figure 3, the opera tion of which will now be described. In the drawing like numbers designate corresponding parts. A lime-char mixture of the previously specified proportions is first prepared in the following manner. Char of 20 to +200 mesh particle size from a fuel hopper is charged to a storage vessel 52. Similarly, regenerated lime or fresh lime of corresponding particle size distribution is transferred from a make-up lime hopper 54 to a storage vessel 56. However, to facilitate the subsequent separation of the lime particles from partially consumed char, it may be desirable to feed char whose particle size range differs from that of the lime, where nevertheless, the particle size range of the bed is within the range of -20 This mixture may be used as the to +200 mesh. For example, relatively coarse lime of -20 to +65 mesh is mixed with --65 mesh char; alternately, 20 to 65 mesh char is fed along with fine lime particles, such as 100 mesh. From these two storage or surge Vessels the char and the lime are conducted under the control of valves 58 and 60, respectively, to charging cylinders 62 and 64 which are sized according to the desired ratio of solids. Then the two batches of solids in the proper weight relation to each other are combined in a conduit 65 whence they'are picked up by a stream of flue gas or low pressure steam from conduit 66 and carried through conduit 61 to a cyclone separator 68. The latter separates the solids from the carrier gas and drops the solids into a solids feed manifold conduit 10. The carrier gas is exhausted through conduit 12. The solids feed manifold 10 is connected to a series of superimposed steam-carbon reaction zones 14 by valved interconnecting conduits 18.

The series of reaction zones 14 may be confined in a single vessel as shown, being separated from one another by imperforate plate members 18. Each of the reaction zones is adapted to contain a bed of solids 19 supported upon a perforated plate member 80. Steam is fed to the several zones below the perforated plate members through valved conduits 82 which communicate with a high pressure steam manifold conduit 84. Solids are discharged from the reaction zones H into a discharge manifold 86 through interconnecting valved conduits 8B which extend down into the beds 18.

In any given cycle some of the reaction zones 74 will not be in operation in order to permit discharge of their contents as will be described below. Those which are in operation to make gas are charged with an amount of lime-char mixture through conduits 16 to establish beds 19 of from one to ten feet in depth. Steam is then introduced below the perforated plate members 80 through conduits 82 and is caused to pass up through the beds 19 at a velocity insufiicient to effect fluidization of the solids. The pressure within the reaction zones is maintained by means of valves 90 disposed in conduits 92 leading to a product gas manifold conduit 94. Steam is passed through the beds of solids in the vessel for from one to four hours or until the lime is substantially converted to carbonate. The composition and heating value of the high pressure product gas issuing through conduit 94 from the reaction vessels [4 correspond substantially to those listed in Table I and given in connection with the description of the operation of the apparatus of Figure 2 for the corresponding temperatures and pressures.

When a reaction zone 14 is not operating to produce the improved gas of this invention, valve 90 in the product gas line 92 is closed and the reaction zone is permitted to communicate with a low pressure low B. t. u. fuel gas product line 96 which is connected to a low pressure gas manifold 98. The gas issuing from manifold 98 can be used directly as a low B. t. u. fuel gas or can be subjected to further processing as will be described later. A valve I00 in conduit 96 is opened during the off cycle of the vessel 14 and closed during the on cycle. In order to discharge the contents of the vessel 14, which after the gas producing cycle comprises largely carbonate mixed with a small amount of ash and unreacted carbonaceous fuel, the pressure is reduced and the velocity of the steam is increased to effect fluidization of the solids supported on distributor plate 80. The valved discharge conduit 08 is then opened and flue gas or steam or other inert gas circulating through conduit I02 draws the solids out of the reaction zone 19 through manifold conduit 86, then through conduit I02 and into a cyclone I04. The solids drop through cyclone leg I06 into a storage vessel I01 while the carrier gas escapes through a conduit I08. When it is desired to replace some of the lime with fresh lime it will be necessary to discharge carbonate from the system and this may be accomplished by a discharge or drawoff conduit H0. The mixture of carbonate and unreacted carbonaceous fuel drops through a valved conduit IIZ into a conduit H4 and is carried by,

means of air into a regenerator H6 in which a fluidized state is maintained by proper control of the linear velocity of the air with respect to the particle size of the solids. Oxidation of the carbonaceous fuel with air in regenerator IIB provides the heat necessary to regenerate the lime. The flue gases leave regenerator H6 through a conduit H1 and enter a cyclone separator Il8 from which they are discharged through effluent line I 20. Separated fines return to the regenerator I I6 through a cyclone leg I2I. Regenerated lime is conducted through a valved conduit I22 to the lime storage vessel 56 for recycling in the above process.

In the regeneration of the lime it is advisable to regulate the air current through the regenerator to prevent undue oxidation of the sulfides formed in the water gas reaction zones 19. When all the carbonaceous solids have been burned, these sulfides may react with excess oxygen to form sulfates unless sufiicient opportunity is provided for their conversion into lime and sulfur, dioxide.

Thus it will be seen that it is possible by the use of a single fluidized regeneration vessel to provide the requisite quantity of fresh lime to a plurality of fixed bed water gas reaction zones. Moreover the production of gas is made continuous by having a series of reaction vessels, some of which are discharging their reacted contents while the remainder are utilized in the manufacture of the desired product gas.

As indicated above, the use of a fluidized steam-carbon reaction zone is feasible provided the pressure is maintained at a relatively low level, i. e., in the neighborhood of the permissible lower limits for this reaction, namely, five to about thirty atmospheres, and also if the beds are of substantial depths to afford adequate contact times. In Figure 4 of the drawings there is shown a completely fluidized system which, subject to the above limitations, is adapted to carry out my new process. This system and its operation will now be described.

Referring to Figure 4 of the drawings, pulverized char from a hopper I50 is fed continuously through a valved conduit I 52 into a reaction vessel I54. Concurrently finely divided lime is continuously charged into reaction vessel I54 through a conduit I56 from a conduit I58. Fresh lime as required is fed from make-up lime hopper I59 into conduit I58. The relative proportions of lime and char are as previously stated. The bed of solids I60 confined in reactor I54 is maintained in a fluidized state by steam fed through conduit I56 from a conduit I62. To effect satisfactory fluidization, the particle size of the solids is preferably less than mesh and the superficial linear velocity of the steam is of the order of 0.1 to 1 foot per second depending on the size distribution of the solids. In order to establish a temperature in the reactor I54 within the range of 1430" to 1800 F., air, instead of steam is first introduced into reactor I54 through a conduit, not shown, to oxidize the char to develop the necessary required temperature. Once this temperature is established, steam replaces the air in order to carry out the steamcarbon reaction and under the conditions maintained in the reactor I54, no further heat need be added. The conversion of water to the steam required by the reaction is accomplished by heat exchangers hereinafter to be described which utilize only the heat developed during the reactions. The pressure in reactor I54 is maintained in accordance with the previously expressed equation relating minimum pressure with temperature but is preferably between ten and thirty atmospheres. Valve I64 in the product gas line I66 serves to control the pressure in reactor I54. Product gas is conveyed from reactor I54 through a conduit I65 to a cyclone I61 where it is separated from entrained solids which are returned to the reaction zone through a cyclone leg I68.

The reactions taking place in the reactor I54 during the gas manufacture are the same as those previously described in connection with the operation of the system illustrated in Figure 2. In this instance, however, instead of regenerating the lime in vessel I54, a mixture of calcium carbonate and char is withdrawn from a settling section I69 through a valved conduit I10 into a valved air line I12. The air carries this mixture of solids through the line I12 into the lime regenerator I14 wherein the lime is regenerated by the heat developed by the oxidation of the char with air. The flow of air through the bed of solids I16 confined in the lime regenerator I14 is regulated so as to maintain a fluidized bed in the same manner as in the reactor I54.

The regenerated lime and ash produced in regenerator I14 are conducted through a valved discharge conduit I18 to a separator I wherein the two solids are separated from each other and from any entrained gases. Ash particles are removed from the system through a valved discharge conduit I8I. The separated lime then is returned through conduit I58 and conduit I56 to the reactor I54. Flue gases from the lime regenerator I14 are conducted through a conduit I82 to a cyclone I84. The precipitated solids are returned to the bed I16 through a cyclone leg I86 while the solid free gases are conducted by a conduit I88 to a conduit I90. Since the gases issuing from the lime regenerator are at an elevated temperature, the heat contained therein is utilized to raise the temperature of the incoming air to the regenerator by passing in heat exchange relation through an exchanger I92. The resulting fiue gases are then conducted through conduit I9! to any suitable place of disposition.

Product gases from reactor I54 contain carbon monoxide, hydrogen, methane and some carbon dioxide, and. as in the' case described in connection with Figure 2, the product is suitable for use as a fuel gas having a composition corresponding to those listed in Table I when produced under similar reaction conditions.

As previously discussed, the reaction conditions in reactor I54 may be regulated to produce either a hydrogen rich gas product or methane rich, high B. t. u. gas product.

Consider first the situation where a hydrogen rich product is desired. Reactor I54 is operated at a pressure only slightly above the pressure given by the empirical relation for minimum thermoneutral pressure. The gas product from reactor I54 contains carbon monoxide, hydrogen, methane and some carbon dioxide in a ratio adapted to produce additional hydrogen by the conventional water gas shift reaction. When a standard water gas shift catalyst, such as iron chromia is employed at about 500 F. in the presence of excess steam, substantially all the carbon monoxide in the gas is converted into carbon dioxide and hydrogen. However, I prefer to run my carbon monoxide conversion reaction in a third vessel containing lime in a fiuidized condition. In this vessel, the carbon monoxide is converted into hydrogen and carbon dioxide. The carbon dioxide formed reacts with the lime, so that the gas product contains more hydrogen than the gas fed into the vessel, a small amount of hydrocarbonaceous gases, predominantly methane and substantially no carbon monoxide or carbon dioxide. Accordingly, the gas produced in vessel I56 is passed through a water gas shift reactor I54 which serves to convert some of the gas to additional hydrogen and to remove some of the carbon dioxide. The heat generated in reactor I94 may be utilized to gencrate steam required to carry out the reaction in vessel I54.

In the present instance, as shown in Figure 4, the product gas from reactor I54 is conducted through conduit I55 into the hydrogen generator I94. Some of the heat contained in the product gas from vessel I54 is utilized in heat exchanger I96 to raise the temperature of the water or steam being fed to the reactor I54 through conduit I52. The hydrogen synthesis in generator I94 can be carried out at about 1431 F. and .at a pressure regulated by valve I53 in the eiliuent gas conduit 200, substantially the same as the pressure maintained in the steam-carbon reactor I54. Lime from separator I80 enters reactor I94 through conduits I58, 2IJI and I66, respectively. Calcium carbonate formed in reactor I94 is discharged from the reaction zone through conduit 203 and returned to the lime regeneration vessel I14 for reconversion to lime. The bed 202 is maintained in a fluidized state by proper sizing of the lime particles and by proper selection of linear velocities of the incoming gases. The resulting hydrogen enriched gas is conducted through a conduit 2% to a cyclone separator 25% from which solid fines are returned to the bed through cyclone leg 208. The substantially solid-free gas product is conducted through conduit 260 to a second cyclone 2H] for removal of any extremely fine solid particles that may have passed through cyclone 205. These solids are removed through valved discharge conduit 2 I2. The gaseous product is carried to storago through a valved conduit 2 I5. The heat con tained in the product gas issuing from the hydrogen generator is utilized in waste heat boiler 225 to raise the temperature of water or steam circulating through conduit I62. The steam or water from the waste heat boiler 22% is conducted in heat exchange relationship with the bed 252 in reaction vessel I94 and from there to heat exchanger I96.

As an example of the further improvement in hydrogen yield effected by the present invention, consider the case in which reactor I54 operates at 1750 F. and 40 atmospheres pressure at a steam conversion rate of 55 per cent. The gas leaving reactor I54 has the following composition:

When this wet product gas is passed through reactor I94 at 1431" F. without the addition of steam, the final product where water gas equilibrium is established in reactor I95, had the following composition on a dry basis:

Volume per cent H2 84.7 CH4 13.4: C0 1.2 CO2 0.7

It may be desirable under certain circumstances to add more steam to the gas feed to reactor I94 thereby increasing the concentration of hydrogen in the final product gas by shifting the equilibrium to favor greater conversion.

A comparison of the hydrogen composition of the final product gas produced by my new invention and that produced by conventional water gas reactions under similar conditions (see Table I) shows the vast improvement which can be realized when the method of the present invention is adopted and when a hydrogen rich gas is desired.

However, as previously discussed, my invention also can be utilized under other conditions to produce methane rich gas which can be upgraded by passing it over any standard mechanization catalyst, such as nickel on aluminum oxide.

The increase in methane content attained by the practice of my process as described is sufficient for many industrial applications. However, I have discovered that a greater increase may be effected if it should be found desirable or necessary, by establishing carefully controlled predetermined temperature difierences in the reaction zone or zones in which the gas is made, the specific temperatures maintained being still within the range previously specified as critical to the successful operation of the process. In this modification of my process, most of the steam-carbon-lime reaction is carried out in a zon where the temperature lies between approximately 1670 and 1770 F. The product gases from this reaction are then caused to circulate through another zone, separate or contiguous, in which the carbonaceous solids are maintained at a temperature between 1430 and 1600" F. While this modified process may be practiced in either a fluidized or non-fluidized system, I have shown an apparatus in Figure 5 for carrying out the process which involves a fluidized system by way of example only.

The operation of the modified system as shown in Figure 5 will now be described. Only the steamcarbon reaction vessel is illustrated since the method of regenerating the lime is the same as any of those previously described. Accordingly, the present description will be restricted to the operation of a reaction vessel 250. The latter is so designed as to provide a plurality of fluidized beds arranged one above the other with the flow of solids from one bed to the other being countercurrent to the flow of fluidizing gas, namely. steam in this instance. In addition, the temperatures of the three beds are maintained so that the temperatures decrease progressively from the bottom to the top. The pressure maintained throughout the system is at least as great as that given above by the empirical relation (2) as the minimum pressure necessary to produce a methane rich gas and is preferably from 30 to 50 atmospheres.

A mixture of char and lime in the previously specified proportions is introduced into the reaction vessel 250 through a conduit 258 into which char is fed from a char hopper 254 and lime is fed from a hopper, not shown, through conduits 256 and 252, respectively. This may be accomplished either by suitable screw feeding devices or by introducing carrier gases such as steam.

The incoming mixture of char and lime forms a bed 260 which is supported on a porous plate 262.. Steam is introduced into the reactor 250 through a conduit 264, circulates up through the vessel and through porous plate 262 into bed 260. The superficial linear velocity of the steam is regulated to effect fiuidization of the solid mixture which is composed of finely divided solids less than 20 mesh size. The mixture of char and lime is fed continuously to bed 260 with the result that the latter builds up until it overflows through a conduit 266 down onto a second porous plate 268. Here in turn a second bed 210 .is established and is likewise maintained in a fluidized condition by the incoming steam. This bed overflows through a conduit 212 to the lower part of the vessel to form a bed 214.

As previously described, it is essential for the operation of my new process that the temperature within the beds lie within the range 1430 to 1800 F. but I have found that a greater yield of methane is produced if most of the reaction between steam and the carbonaceous solids takes place at a temperature between 1670 and 1770 F. with the gaseous product of this reaction thereafter passing through a zone containing carbonaceous solids maintained at a temperature between 1430" and 1600 F., i. e., where the temperature gradient between the two zones is at least 100 F. Accordingly, in the reactor vessel 250, the flow of char and lime mixture through the bed 274 is regulated to maintain a temperature therein between 1670 and 1770 F. The hot product gases and unreacted steam pass up through porous plate 268 through bed 270 where further reaction with steam takes place. However, this bed is maintained at a lower temperature than bed 274 because of the reduction in temperature effected by the relatively cool solids which overflow from bed 268. Additional cooling may be required, 1. e., the gases leaving bed 214 may be cooled by passing over a steam generating coil before entering bed 210. The gaseous products are carried up through porous plate 262 and bed 260 which is maintained at a temperature between 1430 and 1600 F.

Passage of the gaseous products containing carbon monoxide and hydrogen through bed 2611 results in conversion of these gases to methane. The pressure maintained within the vessel is as previously described. A valve 276 in the product gas exit conduit 278 serves to maintain the pressure at the desired level. The product gases are conducted from vessel 258 through a conduit 288 to a cyclone 28l where solid fines are separated 14 and returned to bed 268 through a cyclone leg 286. The solid free product gas leaves the cyclone through conduit 278.

Again as in the apparatus of Figures 2, 3, and 4, the process of Figure 5, carried out under these conditions, is essentially thermoneutral and may be even exothermic. Once the reaction has been started at the temperature and pressure stated, the requisite heat is supplied by the reaction between lime and the product carbon dioxide. The process is maintained continuous by removal of solids containing calcium carbonate and carbonaceous solids from the bottom of the vessel through a conduit 284. The calcium carbonate is regenerated to lime in any of the ways previously described. The product gases obtained from this reactor before being further subjected to methane synthesis have a composition depending upon the particular temperature gradient and the pressure established in the system, but are consistently higher in methane content than those obtained where the reaction zone is held at one temperature. As an example, it was found that where a temperature of 1700 F. was maintained in the lowermost bed, a pressure of 30 atmospheres in the reaction vessel and a temperature between 1430 and 1500 F. in the uppermost bed, a gas was obtained having a gross heating value of 625 B. t. u. per cubic foot at 60 F. and containing 0.6% CO2, 52.1% Hz and 44.1% CH4.

It is to be understood that wherever the word char is used in the foregoing description and in the accompanying claims, it is intended to signify the carbon-containing residue obtained from the low temperature distillation of a hydrocarbonaceous solid fuel.

According to the provisions of the patent statutes, I have explained the principle, preferred construction and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. The method of making water gas which comprises charging lime and a carbonaceous solid fuel to a steam-carbon gasification zone in the relative proportions of at least 120 parts by weight of lime for each parts by weight of carbon contained in said carbonaceous fuel, passing steam in reactive relationship with said carbonaceous fuel in said gasification zone at a temperature within the range 1430 to 1800 F. and under a superatmospheric pressure whose minimum value is determined by the expression where p is the pressure in atmospheres and t is the temperature in F., whereby water gas and calcium carbonate inadmixture with a carbonaceous ash are produced, recovering the water gas, passing air at substantially atmospheric pressure through a mixture of said carbonate and carbonaceous ash while the latter are still at substantially the temperature that prevailed in the gasification zone until substantially all the combustible carbon in said mixture is oxidized, whereby the carbonate is converted to lime and the carbonaceous ash is rendered substantially free of carbon, separating the ash from said regenerated lime and repeating the above cycle with said regenerated lime and fresh carbonaceous fuel.

2. The method according to claim 1 in which the temperature of the gasification zone is between 1520" and 1650 F.

3, The method of making water gas which comprises continuously feeding lime and a carbonaceous solid fuel to a steam-carbon gasification zone in the relative proportions of at least 120 parts by weight of lime for each 100 parts by weight of carbon in said carbonaceous fuel continuously passing steam in reactive relationship with said carbonaceous fuel in said gasification zone at a temperature within the range 1430" to 1800 F. and under a superatmospheric pressure whose minimum value is determined by the expression where p is the pressure in atmospheres and t is the temperature in F., whereby water gas and calcium carbonate in admixture with a carbonaceous ash are produced, recovering the water gas, continuously withdrawing solids comprising said carbonate and carbonaceous ash from said gasification zone and conducting them directly without intentional cooling to a regeneration zone; passing air at substantially atmospheric pressure through .said solids in said regeneration zone, until substantially all the combustible carbon in said solids is oxidized, whereby the carbonate is converted to lime and the carbonaceous ash rendered substantially free of carbon, separating the ash from said regenerated lime, and repeating the above cycle with said regenerated lime and fresh carbonaceous fuel.

4. The method according to claim 3 in which the temperature of the gasification zone is between 1520 and 1650 F.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ellis: Hydrogenation of Organic Substances, 3rd edition, page 738. 

1. THE METHOD OF MAKING WATER GAS WHICH COMPRISES CHARGING LIME AND A CARBONACEOUS SOLID FUEL TO A STEAM-CARBON GASIFICATIONI ZONE IN THE RELATIVE PROPORTIONS OF AT LEAST 120 PARTS BY WEIGHT OF LIME FOR EACH 100 PARTS BY WEIGHT OF CARBON CONTAINED IN SAID CARBONACEOUS FUEL, PASSING STEAM IN REACTIVE RELATIONSHIP WITH SAID CARBONACEOUS FUEL IN SAID GASIFICATION ZONE AT A TEMPERATURE WITHIN THE RANGE 1430* TO 1800* F. AND UNDER A SUPERATMOSPHERIC PRESSURE WHOSE MINIMUM VALUE IS DETERMINED BY THE EXPRESSION 